The present invention relates to an electronic blasting system for use in mining operations and the like, and to a method of blasting using the system.
Pyrotechnic initiation systems for actuating multi-hole blasts are well known. With such systems each hole-to-hole connection carries with it a particular surface delay. By suitable selection of delay times and connection order of in-hole initiators (detonators), a blast designer can achieve a wide range of firing patterns. This approach is sometimes referred to as “delay-by-hook up”. The lead-in line for a blast enters the network of blastholes at the first hole to be fired with connections leading away from this hole delaying each subsequent hole relative to the preceding neighbour. Whilst useful, pyrotechnic blasting systems do however have some fundamental limitations. The main limitations are that pyrotechnic blasting systems provide only a limited range of available delay times and that they suffer from relatively poor accuracy and precision.
In contrast, there now exist electronic detonators that are freely programmable with respect to detonation delay and that are also very accurate with respect to that delay. Electronic detonators are therefore extremely useful in multi-hole blasting operations where individual blastholes are required to detonate (fire) in a predetermined and precise time sequence. The timing sequence is of course known in advance and is programmed into individual detonators based on the position of the detonator in the overall sequence of blasting.
Broadly speaking, when it comes to electronic blasting systems there are two basic techniques used for detonator programming. In the first, electronic detonators are programmed with individual firing times based on their location in the blasting pattern. This requires some deliberate action of an operator (blaster) taking into account the proposed blast design. This may involve keying in of a detonation delay time on a portable programming tool and relaying that delay time to the relevant detonator by some form of communication between the programming tool and the detonator (see, for example, U.S. Pat. No. 6,173,651). Alternatively, where the electronic detonator includes unique identity data associated with it, the identity of the detonator may be associated with a given blasthole into which the detonator is loaded, with individual detonator delay times then being allocated from a central control unit (blast box) using the identity data to address each detonator (see, for example, U.S. Pat. No. 5,894,103). In this case the identity data is invariably captured using a portable reader by visiting each blasthole. As a further alternative, an electronic detonator and the blasthole into which it is loaded may be indirectly associated by linking each with information as to their location. This generally involves an operator visiting each blasthole with a GPS device and logging the coordinates of each hole and the identity data of the detonator allocated to that blasthole. This information is subsequently downloaded and programming effected using a central control unit. These methods tend to be laborious and/or require the use of skilled operators and specialised equipment.
The second technique for programming electronic detonators relies on electrical connections to enable the relative position of detonators to be determined. For instance, systems exist in which a first detonator on a harness line is programmed with that detonator then communicating with the next detonator in order to enable the next detonator to be programmed, and so on. This so-called “daisy chain” programming arrangement does not require each detonator in a blasting arrangement to be visited by an operator but invariably requires an array of electrical connections to be made for the system to operate. Thus, US 2005/0016407 describes a blasting system in which detonators are connected to a programming and control line by four wires attached to (circuitry of) the detonator.
On the other hand, WO 2005/005915 describes a blasting system comprising a 2-wire communication bus line and a separate 2-wire daisy line extending from a control unit. Individual detonators are connected to the communication bus line by one pair of lead wires and to the daisy line by another pair of leads. The use of such systems requiring multiple connections to be made for each detonator can be time consuming and difficult to put into practice, especially in harsh mining environments. Furthermore, increasing the number of connector leads for a detonator increases vulnerability to damage. A number of detonator connector leads could be accommodated in high quality multi-core cables, but this is likely to add significantly to operating costs.
Against this background it would be desirable to provide an electronic blasting system that does not suffer the disadvantages described.